In vehicles in which a fuel cell stack formed by stacking a plurality of fuel-cell cells is used as a drive energy source, a water cooling system (water-cooled fuel cell stack) is generally adopted for cooling the fuel cell stack. In the case of a water-cooled fuel cell vehicle in which a water-cooled fuel cell stack is adopted, air compressed by a high-pressure compressor is usually supplied to the fuel cell stack, and exhaust gas is generally discharged to the outside of the vehicle from an exhaust pipe extended toward the rear side of the vehicle (Patent Literature 1).
FIG. 5 shows a general system configuration of a conventional water-cooled fuel cell vehicle. In a water-cooled fuel cell vehicle system 101 shown in FIG. 5, power generation is performed by a plurality of fuel-cell cells stacked in a water-cooled fuel cell stack 104 in such a manner that compressed hydrogen gas stored in a high pressure hydrogen tank 102 is introduced into an anode intake portion 105 of the water-cooled fuel cell stack 104 via a pressure reducing valve 103, and that, on the other hand, the outside air, which is drawn through a filter 106 and which is used as a reaction gas reacting with hydrogen, is compressed by a compressor 107, so as to be introduced into a cathode intake portion 108 of the water-cooled fuel cell stack 104. After a part of moisture in cathode exhaust gas discharged from a cathode exhaust portion 109 of the water-cooled fuel cell stack 104 is separated by a gas-liquid separator 110, the cathode exhaust gas is discharged to the outside air via a backpressure valve 111 used for controlling the pressure of the cathode system. Further, similarly, anode exhaust gas discharged from an anode exhaust portion 112 of the water-cooled fuel cell stack 104 is also made to pass through a gas-liquid separator 113, and is mixed into the cathode exhaust gas through a purge valve 114. The amount (flow rate) of purge hydrogen exhausted from the anode exhaust portion 112 is sufficiently small as compared with the amount of cathode exhaust gas. For this reason, the purge hydrogen exhausted from the anode exhaust portion 112 can be discharged to the outside air after the concentration of the purge hydrogen is reduced by the cathode exhaust gas to at most the flammable lower limit concentration of 4%. Note that there are also some systems which are configured to recirculate the anode exhaust gas to the anode intake portion 105 by using a hydrogen pump 115.
In a cooling system 116 of the water-cooled fuel cell vehicle system 101, a water pump 117 is provided in a stage preceding or subsequent to the fuel cell in the cooling loop, so as to pressure-feed cooling water. After cooling the water-cooled fuel cell stack 104, the cooling water is subjected to heat exchange with the atmosphere in a radiator 118, and is then again returned to the water-cooled fuel cell stack 104. In the cooling system 116, a heater core 120 for heating the interior of the vehicle compartment and a regulating valve 119, which are connected in series with each other, are provided in parallel with the radiator 118. When the vehicle compartment needs to be heated, the heating is performed by opening the regulating valve 119 to supply high temperature cooling water to the heater core 120 and by driving an air blowing fan 121. However, the amount of waste heat of the water-cooled fuel cell stack 104 is very small as compared with the amount of heat generated by an internal combustion engine, and hence the other auxiliary heat source, such as an electric heater, is generally used in addition to the heater core 120.
The above-described water-cooled fuel cell vehicle system 101 is provided with many auxiliary units including the compressor 107 for compressing the introduced air, in order to increase the output power density of the water-cooled fuel cell stack 104. For this reason, in the water-cooled fuel cell vehicle system 101, the system is complicated, and also the size, weight and cost of the system are increased.
On the other hand, there is an air-cooled fuel cell vehicle in which the system is simplified in such a manner that auxiliary units, such as a compressor, are eliminated as much as possible, and that an air cooling system (air-cooled fuel cell stack) is adopted for cooling the fuel cell stack. In the case of the air-cooled fuel cell vehicle in which an air-cooled fuel cell stack is adopted, air serving as a reaction gas as well as a cooling medium is supplied at a lower pressure by an air supply fan instead of a high pressure compressor (Patent Literature 2).